1. Field of the Invention
The present invention relates to an optical device, an exposure apparatus including the optical device, and a device manufacturing method using the exposure apparatus.
2. Description of the Related Art
An exposure apparatus is used in lithography for manufacturing a device such as a semiconductor device. The exposure apparatus illuminates an original by an illumination optical system, and projects the pattern of the original onto a substrate via a projection optical system, thereby exposing the substrate. An adhesive material is used to fix an optical element on a supporting member in an optical system such as an illumination optical system and projection optical system.
FIGS. 2 and 3 schematically show a partial arrangement of an optical system such as an illumination optical system and projection optical system of an exposure apparatus. An optical element (e.g., a lens or mirror) 2 of the optical system is used while being fixed on an annular supporting member 3. The side portion of the optical element 2 is fixed on the supporting member 3 through an adhesive material 1 (see Japanese Patent Laid-Open No. 2001-242364).
Upon irradiating the optical element of the optical device of the exposure apparatus, light enters positions other than a light propagation portion, which is determined based on the numerical aperture and the angle of view of the optical element, due to diffraction and scattering. For example, as schematically shown in FIG. 3, light which has entered the optical element 2 often reaches the adhesive material 1 upon being transmitted through the optical element 2 and reflected by the supporting member 3. Upon being irradiated with light (typically, ultraviolet rays), the adhesive material connecting the optical element to the supporting member deteriorates, which can result in a decrease in adhesive force and a change in elastic force. This can change the position, orientation, and shape of the optical element, and can therefore decrease the performance of the optical system.